Disclosed herein is an apparatus and method that meters fluid film in an image fusing system that fuses or fixes marking material images onto print media substrates, such as fusing toner onto paper in xerography, or a system that levels or fixes liquid-ink images in ink-jet or offset printing.
Presently, in electrophotographic and other printing processes, an image is typically recorded in the form of a latent electrostatic image upon a photosensitive member. The latent image is subsequently developed on the photosensitive member by applying electroscopic marking particles, commonly referred to as toner. The toner image is then transferred from the photosensitive member to media, such as a sheet of paper. The transferred image is then affixed or fused to the media, for example, by using heat and pressure applied using a fuser assembly, such as a fuser roll or belt.
Polydimethylsiloxane (PDMS) or other release fluid or agent can be used to promote release of the toner and media from the fuser assembly surface, which can extend the usable life of the fuser assembly. Unfortunately, excessive amounts of release fluid on the fuser assembly surface can transfer to the media and contaminate it. Applying a correct amount of release fluid to the fuser assembly using a release agent management system can mitigate transfer to the media, optimize post processing performance, and lower run costs for a user.
For example, fuser assemblies using release fluid can produce 2 to 100 ml of the release fluid on media. High levels of release fluid application on the media is deleterious to achieving good performance for numerous post printing operations, such as hot melt adhesive application for book binding, hot and cold laminating film application, mailing tab and label application, pressure seal application, and other printing operations. Lower release fluid levels broaden the scope of the applications that can be used on prints. On the other end of the spectrum some media demand the higher levels of release fluid on media in order to deliver acceptable fuser assembly life and performance. Unfortunately, release fluid application rates are not adjustable in the machine either automatically or manually.
A release agent management system that controls the amount of release fluid consists of a hard roller and a rubber roller for applying release fluid to the fuser assembly surface. The amount of release fluid is controlled by a metering blade riding the hard roll. This blade is critical for controlling the quality and uniformity of the release fluid. However, blades that produce acceptable films are typically difficult to manufacture, due to the edge quality requirements. Insufficient blade edge quality causes a printing system to become susceptible to producing streaks from high levels or low levels of release fluid. Dry streaks and dirt problems are exacerbated by trying to run the system at low levels of release fluid application.
For example, attempts to reduce the fluid application rate in a conventional release agent management system usually entail making the metering blade edge sharper, reducing the fluid viscosity, increasing the metering blade tip loading, and/or making a metering roller smoother. All of these management attempts can lead to increased frequency of streaks and dirt problems. To elaborate, as the ratio between blade defect size and the nominal fluid film thickness approaches 1:1 and greater, any manufacturing defect in the blade edge produces a wet streak from a hole or depression in the blade, and a dry streak from a protrusion or dirt on the edge of the blade. In addition, sensitivity to dirt and other debris increases as the fluid film thickness is decreased and increased streaking occurs when the debris lodges under a blade contact point at a roller. The streaks can impact image quality and precipitate a service call for release agent management system servicing.
While a fuser fluid reducing roller could be added to a fuser assembly system, problems with such an addition can include spatial constraint problems. A release fluid donor roller in such a system is only so large, which limits the placement position and the number of reducing rollers that can be accommodated within a specific geometry. Furthermore, while additional rollers could be placed around the release fluid donor roller, the additional rollers can hinder the ability to use gravity to return the release fluid to a release agent management pan.
Thus, there is a need for a method and apparatus that meters fluid film in an image fusing system.